The general long-term goal of this program involving heme proteins is to attain an understanding of the molecular mechanisms by which the associated polypeptides interact with a common heme group to produce the remarkable functional diversity which is characteristic of this class of proteins. The essential strategy is to apply powerful spectroscopic probes such as resonance Raman (RR) and time-resolved Raman (TR3) to the native and systematically manipulated proteins in order to reveal the structural and dynamic interactions which regulate heme reactivity. Inasmuch as these proteins are involved in a large number of important physiological processes, including oxygen transport and many types of oxidative metabolic pathways, identification of the factors responsible for this widely varied function would be of obvious benefit for attaining an understanding of their behavior in normal and abnormal states. In the work proposed here an effective strategy recently documented for the native hemoglobin tetramer, which exploits the isotopic sensitivity of molecular vibrations, is being applied to selected site modified hemoglobins. The new data to be accumulated is expected to lead to a better understanding of the molecular mechanism of cooperative ligand binding by hemoglobin, a protein which serves as a paradigm for generally important allosteric processes. In addition, resonance Raman spectroscopy will be used to probe the active site structures of site modified derivatives of oxidative heme enzymes such as cytochromes P450 and mammalian peroxidases, proteins which are important in many metabolic processes and in defense against microorganisms.